JP6224995B2 - FOCUS ADJUSTMENT DEVICE, IMAGING DEVICE, FOCUS ADJUSTMENT METHOD, AND PROGRAM - Google Patents

Description

  The present invention relates to a focus adjustment device, an imaging device, a focus adjustment method, and a program.

  In digital cameras and video cameras, a contrast detection type autofocus (hereinafter referred to as AF) method that uses an output signal from a sensor such as a CCD or CMOS to detect and focus a signal according to the focus evaluation value of the subject. Is commonly used. In this method, the focus evaluation value of the subject is sequentially detected (AF scan operation) while moving the focus lens in the optical axis direction over a predetermined movement range, and the focus lens position where the focus evaluation value is maximized is set as the in-focus position. To detect.

  There is also known an imaging apparatus that performs higher-precision focusing control by selecting an evaluation band of a digital filter for obtaining a focus evaluation value and a sampling interval for performing interpolation calculation of an in-focus position. Yes.

  In Patent Literature 1, a plurality of digital filter evaluation bands for calculating a focus evaluation value are provided, and each focus evaluation value is calculated. By selecting the highest-band digital filter from among the digital filters corresponding to highly reliable evaluation values, the best focus correction amount is reduced, and highly accurate focus detection is possible.

  In Patent Document 2, it is possible to improve the focusing accuracy at the time of interpolation calculation by setting an optimal sampling interval from the optical data, setting parameters (F number, etc.) at the time of shooting, and the evaluation band of the digital filter. is there.

JP 2009-175184 A Japanese Patent No. 3103587

  However, in the conventional technique disclosed in Patent Document 1 described above, since the highest-band digital filter is selected, the evaluation value shape is too steep compared to the sampling interval, and the focusing accuracy may be reduced. There is.

  In the prior art disclosed in Patent Document 2, since the evaluation value shape predicted when setting the sampling interval is performed from the optical design value and the evaluation band of the digital filter, the evaluation value shape obtained by actual measurement and There is a possibility that the focus detection does not match and sufficiently high-precision focus detection cannot be performed.

  The present invention has been made in view of such a situation, and an object thereof is to provide a technique for improving the accuracy of focus adjustment control.

  In order to solve the above-described problems, the present invention provides a focus adjustment unit that performs focus adjustment by moving the position of a focus adjustment member, and an evaluation value acquisition unit that acquires a focus evaluation value based on an output signal of an image sensor. , Control means for causing the focus adjustment means to move the position of the focus adjustment member at a first sampling interval and causing the evaluation value acquisition means to acquire a focus evaluation value corresponding to each position; and a focus corresponding to each position. Based on the evaluation value, the movement amount acquisition means for acquiring the movement amount of the position of the focus adjustment member, which is an index of the steepness of change from the maximum value of the focus evaluation value acquired by the evaluation value acquisition means, An in-focus position is detected based on determination means for determining a second sampling interval based on the amount of movement, and a focus evaluation value corresponding to each position of the focus adjustment member at the second sampling interval. Providing the focusing apparatus characterized by comprising: a detecting means.

  Other features of the present invention will become more apparent from the accompanying drawings and the following description of the preferred embodiments.

  According to the present invention, it is possible to improve the accuracy of focus adjustment control.

5 is a flowchart showing an AF operation procedure of the imaging apparatus 1 according to the first embodiment. The flowchart which shows the calculation procedure of the lens position distance i. 1 is a block diagram illustrating a schematic configuration of an imaging apparatus 1 having a focus adjustment device. The figure which shows AF frame in face detection mode. The conceptual diagram of a process in case sampling interval P 'at the time of performing interpolation calculation is larger than sampling interval P at the time of acquiring a focus evaluation value. The figure which shows a focus evaluation value and its differential value. The figure which shows the relationship between a focus lens position and a focus evaluation value. The conceptual diagram of the interpolation calculation by the linear approximation of a focus position. The conceptual diagram of a focus position in case the maximum value of a focus evaluation value to the 3rd largest value is located in a line. 9 is a flowchart showing an AF operation procedure of the imaging apparatus 1 according to the second embodiment. The figure which shows the focus evaluation value calculated in multiple bands. The figure which shows the relationship between the sampling interval at the time of the interpolation calculation by linear approximation, and a focusing precision. The figure which shows the focus evaluation value shape in the sampling interval with the best focusing precision. The figure which shows the relationship between a sampling phase and the focus position obtained by interpolation calculation.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. The technical scope of the present invention is determined by the claims, and is not limited by the following individual embodiments. In addition, not all combinations of features described in the embodiments are essential to the present invention.

[First Embodiment]
Below, 1st Embodiment is described in detail based on FIG. 1A-FIG. 8 and FIG. 11-FIG. FIG. 2 is a block diagram illustrating a schematic configuration of the imaging apparatus 1 having the focus adjustment apparatus. The imaging device 1 may be, for example, a digital still camera or a digital video camera, but is not limited thereto. For example, the present invention can be applied to any apparatus as long as an incident optical image is acquired as an electrical image by photoelectric conversion using a two-dimensionally arranged solid state sensor such as an area sensor. It is.

  In FIG. 2, 2 is a zoom lens group, 3 is a focus lens group (focus adjustment member), and these constitute a photographing optical system. Reference numeral 4 denotes a stop having a light amount adjustment function (exposure control function) for controlling the amount of light beam transmitted through the photographing optical system. A lens barrel 31 includes a zoom lens group 2, a focus lens group 3, a diaphragm 4, and the like.

  Reference numeral 5 denotes a solid-state sensor (hereinafter referred to as a CCD) such as a CCD that forms a subject image that has passed through the photographing optical system and photoelectrically converts it. The solid state sensor may be a CMOS. In this embodiment, the CCD forms an image sensor.

  Reference numeral 6 denotes an image pickup circuit that receives an electrical signal photoelectrically converted by the CCD 5 and performs various image processing to generate a predetermined image signal. Reference numeral 7 denotes an A / D conversion circuit that converts an analog image signal generated by the imaging circuit 6 into a digital image signal.

  Reference numeral 8 denotes a memory (SDRAM) such as a buffer memory for temporarily storing a digital image signal output from the A / D conversion circuit 7. The SDRAM 8 forms a storage unit in the present embodiment. The SDRAM 8 can record an output signal of a partial area of the imaging area of the CCD 5. A scan AF processing circuit 14 to be described later can perform focus detection by acquiring an output signal recorded by the SDRAM 8 via the MPU 15. Reference numeral 9 denotes a D / A conversion circuit that reads an image signal stored in the SDRAM 8 and converts it into an analog signal and converts it into an image signal in a form suitable for reproduction output.

  Reference numeral 10 denotes an image display device (hereinafter, LCD) such as a liquid crystal display device (LCD) for displaying image signals. Reference numeral 12 denotes a recording memory that records image data including a semiconductor memory or the like. Reference numeral 11 denotes a compression / expansion circuit including an expansion circuit that performs a decoding process, an expansion process, and the like. The compression / decompression circuit 11 also includes a compression circuit that reads out the image signal temporarily stored in the SDRAM 8 and performs compression processing and encoding processing of the image data in order to obtain a form suitable for recording in the recording memory 12. The compression / decompression circuit 11 is configured to perform processing necessary for reproducing and displaying the image data recorded in the recording memory 12.

  Reference numeral 13 denotes an AE processing circuit that receives an output from the A / D conversion circuit 7 and performs automatic exposure (AE) processing. Reference numeral 14 denotes a scan AF processing circuit that receives an output from the A / D conversion circuit 7 and performs autofocus (AF) processing.

  Reference numeral 15 denotes an MPU having a built-in memory for controlling the image pickup apparatus 1. Reference numeral 16 denotes a timing generator (hereinafter referred to as TG) that generates a predetermined timing signal.

  Reference numeral 17 denotes a CCD driver. Reference numeral 21 denotes an aperture drive motor that drives the aperture 4. Reference numeral 18 denotes a first motor driving circuit for driving and controlling the diaphragm driving motor 21. A focus drive motor 22 drives the focus lens group 3. Reference numeral 19 denotes a second motor drive circuit that drives and controls the focus drive motor 22. A zoom drive motor 23 drives the zoom lens group 2. Reference numeral 20 denotes a third motor drive circuit for driving and controlling the zoom drive motor 23.

  An operation switch (SW) 24 includes various switch groups. An EEPROM 25 is an electrically rewritable read-only memory in which programs for performing various controls, data used for performing various operations, and the like are stored in advance. Reference numeral 26 denotes a battery, 28 denotes a strobe light emitting unit, 27 denotes a switching circuit that controls flash light emission of the strobe light emitting unit 28, and 29 denotes a display element such as an LED for displaying OK / NG of AF operation.

  A recording memory that is a recording medium for image data or the like is a fixed semiconductor memory such as a flash memory, and has a card shape or a stick shape. In addition to a semiconductor memory such as a card-type flash memory that is detachably formed with respect to the imaging apparatus 1, various forms such as a magnetic recording medium such as a hard disk and a flexible disk can be employed.

  The operation switch 24 includes a main power switch, a release switch, a reproduction switch, a zoom switch, a switch for turning on / off the display of the AF evaluation value signal on the monitor, and the like. The main power switch is for starting up the imaging apparatus 1 and supplying power. The release switch causes the imaging apparatus 1 to start a shooting operation (recording operation) or the like. The reproduction switch causes the imaging apparatus 1 to start a reproduction operation. The zoom switch moves the zoom lens group 2 of the photographing optical system to perform zooming. The release switch has a first stroke (hereinafter referred to as SW1) for generating an instruction signal for starting AE processing and AF processing performed prior to a photographing operation and a second stroke (hereinafter referred to as an instruction signal for starting actual exposure operation). , SW2) and a two-stage switch.

  Next, with reference to FIG. 1A, the focusing operation (AF operation) by the imaging apparatus 1 having the above-described configuration will be described. FIG. 1A is a flowchart illustrating an AF operation procedure of the imaging apparatus 1. A control program related to this operation is executed by the MPU 15. When the imaging apparatus 1 starts the AF operation, the process of this flowchart starts.

  In S101, the MPU 15 sets an AF frame. For example, as shown in FIG. 3, the MPU 15 sets the position and size of a frame for performing AF in the entire image area. The position and size of the AF frame may be arbitrarily determined according to the shooting mode. FIG. 3 is a conceptual diagram when an AF frame is set in accordance with a human face in the face detection mode. The MPU 15 stores the position and size of the AF frame at this time.

  In S102, the MPU 15 determines the sampling interval P (scan interval of the focus lens group 3) and the number of scans N for performing the AF scan (focus detection operation) with the AF frame set in S101.

  In general, when a focus position search is performed by changing the sampling interval a plurality of times, first, the sampling interval is set wide to find a rough focus position (rough scan). Thereafter, the vicinity of the in-focus position found by the coarse scan is scanned at a finer sampling interval than during the coarse scan (fine scan).

  In S103, the MPU 15 initializes a variable n for counting the number of scans to 1.

  In S104, the MPU 15 controls the second motor driving circuit 19 to move the focus lens group 3 to the scan start position. Then, the MPU 15 calculates and stores the focus evaluation value Ev [1] at the current scan position by using the scan AF processing circuit 14.

  In S105, the MPU 15 adds 1 to n. In S106, the MPU 15 determines whether or not n> N. If n> N is not the case, the process returns to S104, and the MPU 15 controls the second motor drive circuit 19 to move the focus lens group 3 by the sampling interval P and calculate the focus evaluation value Ev [n]. Thereby, focus evaluation values Ev [n] (n = 1, 2, 3,..., N) at each scan position from the scan start position to the scan end position are obtained.

  FIG. 6 shows the relationship between the focus lens position LP [n] corresponding to each scan position and the focus evaluation value Ev [n]. FIG. 6 shows a change in the focus evaluation value Ev [n] when the focus lens group 3 is moved from the focus lens position LP1 to LP10 at the sampling interval P. The focus evaluation value Ev is a parameter that takes a larger value as the focus state is closer. In FIG. 6, the focus lens position LP6 is closest to the focus position. In this case, a focused image can be acquired by driving the focus lens group 3 to a position LP_P in the vicinity of LP6 obtained by interpolation calculation (details will be described later).

  In S107, the MPU 15 calculates a distance (lens position distance i) between the focus lens position corresponding to the maximum focus evaluation value and the focus lens position corresponding to the inflection point of the focus evaluation value. Details of the calculation process (the lens position distance i is also referred to as “movement amount acquisition process” because it corresponds to the amount of movement of the lens between the two positions) will be described later with reference to FIG. 1B.

  In S108, the MPU 15 calculates the sampling interval P ′ by P ′ = (i × M) P. Here, the sampling interval P ′ is a sampling interval for calculating the focus lens position LP_P which is the final in-focus position. M is a coefficient. The magnitude of the coefficient M may vary depending on the interpolation calculation method (described later) of the focus lens position LP_P, or experimentally, the sampling interval that provides the best focusing accuracy and the lens position distance i at that time. It may be a value obtained from the size. Further, when the value of i × M cannot be realized at the actual sampling interval, P ′ may be made an integral multiple of P by rounding off to i × M ([i × M + 0.5]). Alternatively, the focus evaluation value may be acquired again at the sampling interval P ′ calculated by (i × M) P by driving the focus lens group 3 again.

  FIG. 11 shows the relationship between the sampling interval and the focusing accuracy at the time of interpolation calculation by linear approximation. In FIG. 11, it is assumed that the focus evaluation value Ev is obtained as shown in FIG. 6, the dotted line shows the relationship between the sampling interval and the focusing accuracy when there is no noise, and the solid line shows the case when there is noise. The relationship between sampling interval and focusing accuracy is shown. In the graph of FIG. 11, the vertical axis shows higher focusing accuracy as it goes down. Since the actual focus evaluation value Ev is affected by sensor noise on the CCD 5 and does not change as a function, the actually obtained evaluation value shape takes a shape close to the solid line in FIG. Further, since the interpolation calculation result is more easily affected by the variation in the focus evaluation value Ev for each point as the sampling interval is smaller, the focusing is performed when the sampling interval is narrow as shown by the solid line in FIG. Accuracy deteriorates. In FIG. 11, the sampling interval P ′ corresponding to the minimum value does not change depending on the amount of noise. Therefore, the focusing accuracy can be improved by performing the interpolation calculation at the sampling interval P ′.

  In general, in the interpolation calculation by linear approximation, the sampling interval with the best focusing accuracy is correlated with the lens position distance i described above, and the size of the sampling interval is 1 of the lens position distance i. About 4 times. That is, the above-mentioned coefficient M can be set to 1.4. As shown in FIG. 12, when the sampling interval P ′ set from the lens position distance i is used, the calculated focus lens position LP_P is usually calculated using a phase indicated by a circle in addition to a phase indicated by a cross and a triangle. Becomes close to the actual in-focus position. As described above, when a sampling interval P ′ having a size M times the lens position distance i is used, the center of gravity of the three points created by the linear approximation always captures the vicinity of the in-focus position. Accuracy is improved.

  Returning to FIG. 1A, in S109, the MPU 15 performs interpolation calculation at the sampling interval P 'calculated in S108 to obtain the focus lens position LP_P. An example of a method of interpolation calculation by linear approximation will be described with reference to FIG. The method based on the linear approximation has a smaller calculation load than the focus detection method based on the higher-order approximation. Further, the method based on the linear approximation has an advantage of being resistant to noise because the lens position near the maximum value of the focus evaluation value can be detected even when the focus evaluation value shape near the focus position has many variations.

  FIG. 7 is an enlarged view of the vicinity of the in-focus position in FIG. At this time, there are various methods for obtaining the focus lens position LP_P, but this embodiment relates to a method for calculating the focus lens position LP_P by linear approximation. Hereinafter, the focus lens position LP_P obtained by linear approximation may be referred to as a focus position LP_P or an interpolation focus position LP_P.

An example of obtaining the interpolation focus position LP_P by linear approximation will be described. When obtaining the interpolation focus position LP_P, first, the MPU 15 first determines the maximum focus evaluation value (Ev [6] in FIG. 7), the second largest value (Ev [5]), and the third largest value ( Ev [7]) and its lens positions LP6, LP5, L7 are detected. At this time, first, an equation of a straight line L1 passing through Ev [6] and Ev [7] is obtained. L1 is x on the horizontal axis and y on the vertical axis.

L1: y = ((Ev [7] −Ev [6]) / (LP7−LP6)) × x + ((LP7 × Ev [6] −LP6 × Ev [7]) / (LP7−LP6))

Can be obtained.

Next, an equation of a straight line L2 passing through Ev [5] with the sign of the slope of L1 being opposite is obtained. Similarly, if the horizontal axis is x and the vertical axis is y, L2 is

L2: y = − ((Ev [7] −Ev [6]) / (LP7−LP6)) × x + Ev [5] + ((Ev [7] −Ev [6]) / (LP7−LP6)) × LP5

Can be obtained.

At this time, the x coordinate of the intersection of L1 and L2 becomes the interpolation focus position LP_P. That means

LP_P = (Ev [5] + ((Ev [7] −Ev [6]) / (LP7−LP6)) × LP5 − ((LP7 × Ev [6] −LP6 × Ev [7]) / (LP7− LP6))) / (2 × ((Ev [7] -Ev [6]) / (LP7-LP6)))

It becomes. Here, a method of performing linear approximation from three points is shown, but it may be performed from four points. Alternatively, as shown in FIG. 8, when the maximum value to the third largest value are arranged in a line, the lens position LP6 taking the maximum value Ev [6] is set to LP_P. May be performed.

  FIG. 4 is a conceptual diagram of processing when the sampling interval P ′ when performing the interpolation calculation is larger than the sampling interval P when the focus evaluation value Ev [n] is acquired. In this example, the focus evaluation value Ev [n] at each focus lens position LP [n] is acquired. Conventionally, interpolation calculation is performed as shown in FIG. 7 using the lens positions LP5, LP6, LP7 and their evaluation values Ev [5], Ev [6], Ev [7]. On the other hand, in this embodiment, LP_P is obtained by performing interpolation calculation at a sampling interval P ′ that is a constant multiple of the lens position distance i (or an integer closest thereto). In FIG. 4, the lens positions LP1, LP5, LP9 and their evaluation values Ev [1], Ev [5], Ev [9] are used. At this time, the lens positions LP2, LP6, LP10 having different phases and the evaluation values Ev [2], Ev [6], Ev [10] may be used. Or it is good also considering the average value of several LP_P calculated by phase difference as final LP_P. Note that the difference in phase means that the start positions of sampling (acquisition of evaluation values) at the sampling interval P ′ are different.

  The reason why the focusing accuracy is further improved by using the average value of the interpolation calculation result of the phase difference will be described with reference to FIG. In general, assuming that the sampling interval when acquiring the focus evaluation value for the first time is P and the sampling interval when calculating the focus position by interpolation calculation is P ′, the focus position is n = P ′ / P phases. LP_P ′ can be calculated. The relationship between the sampling phase n and LP_P ′ at this time is shown in FIG. Since the position where the vertical axis is 0 indicates the actual in-focus position, the average of interpolation calculation results in a plurality of phases can increase the possibility of approaching the actual in-focus position.

  Returning to FIG. 1A, in S110, the MPU 15 controls the second motor drive circuit 19 to move the focus lens group 3 to the in-focus position LP_P obtained in S109. As a result, a series of AF operations are completed.

  Next, a method for calculating the lens position distance i will be described in detail with reference to FIGS. 1B and 5. In S151, the MPU 15 calculates the differential value dx [1] of the focus evaluation value Ev [1] by dx [1] = Ev [2] −Ev [1].

  In S152, the MPU 15 initializes both the maximum value Max_dx and the minimum value 0_dx of differential values to | dx [1] |. Further, the MPU 15 initializes variables Max_xdx and 0_xdx indicating the focus lens positions corresponding to Max_dx and 0_dx to 1. In S153, the MPU 15 initializes the variable n to 2.

  In S153 to S160, the MPU 15 calculates dx [N−1] from dx [2] by dx [n] = Ev [n + 1] −Ev [n]. Here, N is the value determined in S102 of FIG. 1A, and is 10 in this embodiment. Further, the MPU 15 updates Max_dx and 0_dx as needed (see the conditional branches in S155 and S157).

  The upper side of FIG. 5 shows Ev [1] to Ev [10] calculated in S104 of FIG. 1A, and the lower side of FIG. 5 shows dx [1] to dx [1] calculated in S151 and S154 of FIG. 9]. When dx [9] is obtained from dx [1] as shown in the lower part of FIG. 5, Max_dx = | dx [3] | and 0_dx = | dx [6] | are finally obtained. As shown in S156 and S158 of FIG. 1B, when the MPU 15 updates Max_dx and 0_dx, Max_xdx and 0_xdx are also updated with n at that time. Therefore, finally, Max_xdx = 3 and 0_xdx = 6.

  In S161, the MPU 15 is the distance between the focus lens position corresponding to the maximum value of the focus evaluation value and the focus lens position corresponding to the inflection point of the focus evaluation value by i = | Max_xdx-0_xdx | The lens position distance i is calculated. In the example of FIG. 5, i = 3 is obtained.

  In the above description, it is assumed that Max_xdx and 0_xdx are the values of n when Max_dx and 0_dx are updated. However, the MPU 15 may obtain Max_xdx and 0_xdx by linear interpolation based on a plurality of points including the maximum focus evaluation value or the inflection point. For example, in the example of FIG. 5, it is considered that the true maximum value of the focus evaluation value is not at the position of n = 6 but at a position between n = 6 and n = 7. Therefore, the MPU 15 obtains a value of 0_xdx by high-order approximation or linear interpolation based on dx [5], dx [6], and dx [7] and n = 5, 6, and 7 corresponding to these. be able to. In this case, the lens position distance i may be a decimal value instead of an integer.

  In the above description, the method of calculating the inflection point of the focus evaluation value using the differential value has been described. However, the minimum value of the secondary differential may be used. Also, at the base of the evaluation value (far from the in-focus position), the differential value takes a small value, so if the amount of change in the focus evaluation value continues below a certain value, it is excluded from the inflection point calculation. May be.

  As described above, according to the first embodiment, the imaging apparatus 1 acquires N focus evaluation values Ev [n] based on the sampling interval P and the number of scans N. Then, the imaging apparatus 1 calculates a lens position distance i that is a distance between the focus lens position corresponding to the maximum focus evaluation value and the focus lens position corresponding to the inflection point of the focus evaluation value. Then, the imaging apparatus 1 calculates the sampling interval P ′ based on the lens position distance i and the coefficient M, and calculates the final in-focus position by interpolation calculation based on the sampling interval P ′.

  The lens position distance i is an index indicating the shape (steepness) of the focus evaluation value, and corresponds to the amount of movement of the focus lens group 3 (distance between two positions). By determining the sampling interval P ′ based on the lens position distance i having such properties, the accuracy of the in-focus position interpolation calculation is improved. Therefore, according to the present embodiment, it is possible to improve the accuracy of the focus adjustment control.

  In the above description, as an index indicating the shape (steepness) of the focus evaluation value, the focus lens position corresponding to the maximum value of the focus evaluation value and the focus lens position corresponding to the inflection point of the focus evaluation value. The lens position distance i, which is the distance between them, was used. However, instead, for example, the lens position distance corresponding to the half-value width of the focus evaluation value may be used as an index. Any index may be used as long as it is an index that can be used when determining the sampling interval P ′ that improves the accuracy of the interpolation calculation of the in-focus position.

[Second Embodiment]
Hereinafter, the second embodiment will be described with reference to FIGS. 9 and 10. In the second embodiment, calculation of focus evaluation values in a plurality of bands is performed. In the present embodiment, the basic configuration of the imaging apparatus 1 is the same as that of the first embodiment (see FIG. 2).

  With reference to FIG. 9, the focusing operation (AF operation) by the imaging apparatus 1 will be described. FIG. 9 is a flowchart illustrating an AF operation procedure of the imaging apparatus 1. 9, steps in which the same or similar processing as in FIG. 1A is performed are denoted by the same reference numerals as in FIG. 1A, and description thereof is omitted.

  In step S901, the MPU 15 initializes a variable k indicating a filter number to 1. The imaging apparatus 1 has K filters having different passbands, and the focus evaluation value is calculated based on a signal processed by any of these filters. In this embodiment, K = 3.

  In S902, the MPU 15 selects the kth filter (filter [k]). In S903, the MPU 15 uses the scan AF processing circuit 14 to calculate the focus evaluation value AF_C [k] [n]. The processing here is substantially the same as S104 in FIG. 1A, but differs from S104 in that the calculation is performed based on the signal processed by the filter [k].

  In S904, the MPU 15 adds 1 to k. In S905, the MPU 15 determines whether or not k> K. If not k> K, the process returns to S902, and the MPU 15 selects another filter and repeats the same process.

  A focus evaluation value as shown in FIG. 10 is acquired by the processing from S901 to S905, S105, and S106. In general, when low-band filter processing is performed, a gentle evaluation value that can detect a change in the focus evaluation value at a wide focus lens position with a small amount of change in the focus evaluation value as in AF_C [1]. A shape is obtained. Conversely, when high-band filter processing is performed, as in AF_C [3], the amount of change in the focus evaluation value increases near the in-focus position, and a steep evaluation value shape is obtained.

  In S906, the MPU 15 calculates a lens position distance i [k] (k = 1 to K). The processing here is substantially the same as S107 in FIG. 1A, but the lens position distance for each of the K filters is based on the corresponding focus evaluation value AF_C [k] [n] (n = 1 to N). Calculated. As shown in FIG. 10, since the shape becomes steeper as the evaluation value calculated in the high band, the lens position distance i [k] takes a small value. As described in the first embodiment, when linear interpolation or the like is performed, the lens position distance i [k] may be a decimal number. In FIG. 10, i [2] is a decimal number.

In S907, the MPU 15 determines a filter and a sampling interval P ′ to be used when calculating the in-focus position based on the lens position distance i [k] calculated in S906. This selection will be described with reference to FIG. As shown in FIG. 10, it is assumed that focus evaluation values in three types of filter bands are obtained at the sampling interval P, respectively. At this time, i [1], i [2], and i [3] are values shown in the lower part of FIG. At this time, as described in the first embodiment, the sampling interval P ′ used for in-focus position calculation is:
P ′ = (i [k] × M) P (M = constant)
I [k] × M should be an integer. In the example of FIG. 10, when M = 1.4, when k = 2, i [k] × M = 2 (ie, P ′ = 2P). Therefore, the MPU 15 selects the filter [2] and sets the sampling interval P ′ = 2P. More generally speaking, the MPU 15 determines a final P ′ that is closest to an integer multiple of P among P ′ corresponding to each filter. However, when the closest integer multiple of P is not a perfect integer multiple of P, the MPU 15 determines that the closest integer multiple of P and the perfect integer multiple of P is the final P ′. decide.

  In S908, the MPU 15 performs interpolation calculation on the focus evaluation value acquired corresponding to the filter selected in S907 at the sampling interval P 'determined in S907 to obtain the focus lens position LP_P. The specific calculation method here is the same as S109 of FIG. 1A.

  As described above, the MPU 15 determines the filter and the sampling interval P ′ based on the condition that the multiplication value of the constant M and the lens position distance i [k] is closest to the integer value. When there are a plurality of filters that satisfy the condition, the MPU 15 may select a filter with the smallest P ′. Alternatively, the MPU 15 may calculate the saving position in S908 using each of the plurality of filters, and set the average value as the final focusing position. When P ′ is 2 or more, as described in the first embodiment, the MPU 15 performs calculation with a plurality of phases when calculating the in-focus position in S908, and calculates the average value as the final value. It is good also as a general focus position.

  As described above, according to the second embodiment, the imaging apparatus 1 calculates focus evaluation values in a plurality of bands, and selects a filter in a band that most improves the focusing accuracy. Thereby, it is possible to improve the accuracy of the focus adjustment control.

[Other Embodiments]
In the above embodiment, the change of the focus state of the subject is realized by the movement of the focus lens group 3. However, the method for realizing the change of the in-focus state is not limited to this. For example, the focus state may be changed by moving the CCD 5 instead of the focus lens group 3. In this case, the CCD 5 serves as a focus adjustment member. In addition, as long as the imaging apparatus can acquire the incident angle information (light field information) of the light beam, the focus state may be changed by reconstruction processing.

  The present invention can also be realized by executing the following processing. That is, software (program) that realizes the functions of the above-described embodiments is supplied to a system or apparatus via a network or various storage media, and a computer (or CPU, MPU, etc.) of the system or apparatus reads the program. It is a process to be executed.

Claims (10)

Focus adjusting means for adjusting the focus by moving the position of the focus adjusting member;
Evaluation value acquisition means for acquiring a focus evaluation value based on an output signal of the image sensor;
Control means for causing the focus adjustment means to move the position of the focus adjustment member at a first sampling interval, and for causing the evaluation value acquisition means to acquire a focus evaluation value corresponding to each position;
Based on the focus evaluation value corresponding to each position, the amount of movement of the position of the focus adjustment member, which is an indicator of the steepness of change from the maximum value of the focus evaluation value acquired by the evaluation value acquisition means, is acquired Movement amount acquisition means;
Determining means for determining a second sampling interval based on the amount of movement;
Detection means for detecting a focus position based on a focus evaluation value corresponding to each position at the second sampling interval of the focus adjustment member;
A focus adjusting apparatus comprising: The detection means moves the position of the focus adjustment member at the second sampling interval in the focus adjustment means, and causes the evaluation value acquisition means to acquire a focus evaluation value corresponding to each position, thereby adjusting the focus adjustment. The focus adjustment apparatus according to claim 1, wherein a focus evaluation value corresponding to each position of the member at the second sampling interval is acquired. The determining means determines the second sampling interval so that the second sampling interval is an integral multiple of the first sampling interval;
The detection means obtains a focus evaluation value corresponding to each position of the focus adjustment member at the second sampling interval from a focus evaluation value corresponding to each position of the focus adjustment member at the first sampling interval. The focus adjustment apparatus according to claim 1, wherein the focus adjustment apparatus is obtained. Filter means for selecting one of a plurality of bands and passing the selected band of the output signal of the image sensor;
The determining means includes
A second sampling interval is determined for each movement amount acquired by the movement amount acquisition unit based on the focus evaluation value acquired by the evaluation value acquisition unit in a state where each of the plurality of bands is selected,
The second sampling interval corresponding to each of the plurality of bands is selected to be the closest to an integer multiple of the first sampling interval, and is an integer multiple of the first sampling interval and the selected second A value closest to the sampling interval is determined as the final second sampling interval,
The detection means detects the in-focus position based on a focus evaluation value acquired by the evaluation value acquisition means in a state where a band corresponding to the final second sampling interval is selected. The focus adjusting apparatus according to claim 1. The detection means includes
Using a plurality of different positions as start positions, a focus evaluation value corresponding to each position at the second sampling interval of the focus adjustment member is obtained for each start position,
For each start position, a focus position is detected based on a focus evaluation value corresponding to each position at the second sampling interval of the focus adjustment member;
The focus adjustment apparatus according to any one of claims 1 to 4, wherein an average value of focus positions corresponding to the start positions is detected as the final focus position. The movement amount acquisition means includes the position of the focus adjustment member corresponding to the maximum value of the focus evaluation value acquired by the evaluation value acquisition means and the focus adjustment member corresponding to the inflection point of the change of the focus evaluation value. The focus adjustment apparatus according to claim 1, wherein a distance from the position of the focus position is acquired as the amount of movement. The movement amount acquisition unit acquires, as the movement amount, a distance between positions of the focus adjustment member corresponding to a half-value width of the focus evaluation value acquired by the evaluation value acquisition unit. The focus adjustment apparatus according to any one of 1 to 6. The focus adjustment device according to any one of claims 1 to 7,
The imaging element;
An imaging apparatus comprising: A focus adjustment method using a focus adjustment device,
A focus adjusting step in which the focus adjusting means of the focus adjusting device adjusts the focus by moving the position of the focus adjusting member;
An evaluation value acquisition unit for acquiring an evaluation value based on an output signal of the image sensor, wherein the evaluation value acquisition unit of the focus adjustment device,
A control step in which the control means of the focus adjustment apparatus moves the position of the focus adjustment member at a first sampling interval by the focus adjustment step, and acquires a focus evaluation value corresponding to each position by the evaluation value acquisition step; ,
The movement amount acquisition means of the focus adjustment device is an index of steepness of change from the maximum value of the focus evaluation value acquired by the evaluation value acquisition step based on the focus evaluation value corresponding to each position. A movement amount acquisition step of acquiring a movement amount of the position of the focus adjustment member;
A determination step in which a determination unit of the focus adjustment apparatus determines a second sampling interval based on the movement amount;
A detecting step in which the detection means of the focus adjustment device detects a focus position based on a focus evaluation value corresponding to each position of the focus adjustment member at the second sampling interval;
A focus adjustment method comprising:   The program for functioning a computer as each means of the focus adjustment apparatus of any one of Claims 1 thru | or 7.

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